Previously, hard contact lenses were the only type available, and while such lenses required cleaning, sterilization was not a particular problem. The soft contact lenses which have now been developed are made from a porous plastic material which absorbs water, and upon doing so becomes soft and pliable. While hard lenses must be cleaned and sterilized periodically, the need for sterilization of the soft lenses is more acute, this being due to the porous nature of the plastic material which provides a medium for bacteria. Therefore, the soft contact lenses should be cleaned and sterilized on a regular basis, perhaps daily.
Since the soft lens material is permeable to liquids, soaking soft lenses in strong germicidal solutions for sterilizing purposes is not desirable. This is because such soaking will result in the lense becoming impregnated with the solution, and this can lead to irritation to the eyes when the lenses are worn. In general, it has been found difficult, if not impossible, to disinfect soft lenses by treatment with chemical or biochemical solutions since such solutions have been found to cause eye irritation to at least a substantial percentage of the users.
Accordingly, another sterilization method has been developed for soft lenses, and which involves placing the lenses in a saline solution, and the heating of the saline solution to a temperature sufficiently high to destroy any bacteria that might be present on the lenses. In carrying out this method, and in accordance with the prior art practice, the lenses are placed in a case which contains the saline solution, and the case is placed in a second vessel containing water, or other fluid, which is heated by any appropriate heating element. Or, alternately, the lenses are disposed within the case containing the saline solution, and the case is placed in direct contact with the heating element.
The unit of the present invention goes a step further, and provides for the case itself, which contains the saline solution, to be incorporated into the housing for the heating element, so that a compact unit may be provided which can be easily carried about by the user.
As mentioned above, for disinfecting soft contact lenses, the heat of the saline solution must be raised to an elevated temperature sufficient to destroy any bacteria that might be in the lens, and the heating unit must hold the temperature of the lens at or above that temperature for the required time, and then allow the temperature to cool to ambient level. Typical values of the time and temperature deemed suitable for disinfecting soft contact lens require the lens to be maintained at or above 80.degree. C. for a period of 10 minutes or more. Since aging of the lens material is accelerated by excessive temperatures and/or by extended time at elevated temperatures, it is desirable that the heating unit be controlled so that excessive temperatures, or excessive time at elevated temperatures will not shorten the life of the lens. This is achieved by the unit described in U.S. Pat. No. 4,158,126, which is licensed to the present assignee.
The sterilization unit of the present invention is of the same general type described and claimed in U.S. Pat. No. 4,158,126, and like the unit described in the patent, uses a fluid, such as wax to transmit heat from the heating element to the saline solution containing case for the contact lenses. However, as described above, the unit of the present invention, unlike the unit described in the patent, and unlike other prior art contact lense disinfecting units, provides for the contact lens case to be part of the heating unit, so that a compact unit may be provided which is readily portable, and which may be carried, for example, in a purse or handbag.